Conventional semiconductor processing involves implanting or depositing regions or layers of different material either into or on different regions of a semiconductor substrate. To ensure that the material is positioned at the correct location on the semiconductor substrate, a photo imaging process is conventionally used to define the regions that will subsequently receive the material. The conventional photo imaging process, known as photolithography, may involve projecting light waves onto a photoresist surface so that the light reacts with the photoresist to create an imaged pattern. The photoresist may then be selectively removed as a result of the exposure such that a region of the semiconductor device is exposed to receive the additional material.
In some cases, light waves propagate through the photoresist, reach the underlying substrate, and reflect from the substrate surface back through the photoresist. The reflected light can interfere with other waves propagating through the photoresist and ultimately reduce the accuracy and precision of the image being transferred. In particular, the reflected light can interfere and scatter light waves that are being directed toward a particular region of the photoresist which in turn reduces the effectiveness of exposure intended for the region. As a consequence, the region of the photoresist may not be as uniformly exposed and selective removal of the photoresist during subsequent processing steps may be affected. Furthermore, light reflected from the substrate surface can scatter, especially if the substrate surface is non-planar, such that the scattered light can inadvertently expose the photoresist surrounding the desired region of the photoresist. Thus, the reflected light can expose regions of the photoresist that should otherwise remain unexposed, which limits the ability to precisely define regions of the photoresist for selective removal.
To address this particular problem associated with the photo imaging process, antireflective coatings or layers are commonly used to attenuate or absorb the light waves reflected from the substrate surface during photo exposure operations. Antireflective coatings are materials generally known for their ability to absorb various wavelengths of radiation. They are conventionally interposed between the substrate surface and the photoresist so as to serve as a barrier that inhibits the reflected waves from traversing back through the photoresist and adversely affecting the imaging process. Dielectric antireflective coating (DARC) and bottom antireflective coating (BARC) are examples of antireflective materials that are commonly used to absorb radiation reflected from the substrate surface during the photo imaging operations of integrated circuit processing.
Conventional BARC and DARC layers do not attenuate or absorb all of the light waves and are most effective at absorbing light received from a single angle. In an attempt to improve efficiency of antireflective coatings, double-layer coatings of thin films of SiO, CeO2 and ZnS formed by vacuum evaporation have been utilized. A single-layer antireflective coating may be, for example, 90% effective at absorbing reflected light. A second antireflective coating would absorb 90% of the light that passes through the first single-layer antireflective layer. Thus, a multilayer antireflective coating exponentially increases the amount of reflected light that may be absorbed. However, such structures are cost prohibitive and time intensive as each layer must be individually deposited. Antireflective coatings are also used in other applications and devices such as CMOS imagers and optical devices, with similar limitations. Accordingly, there is a need for affordable multilayer antireflection coatings that may be formed efficiently.